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Sabtu, 12 Juni 2010

In the tundra, conditions are cold, with an annual average temperature less than 5° C, and precipitation (mostly in the form of snow) less than 100mm per year (see figure at right). The summer is brief, with temperatures above freezing lasting for only a few weeks at most. However, this "warm" summer coincides with periods of almost 24 hour daylight, so plant growth can be explosive.

World Distribution:

The map below shows the tundra spreading across the northern hemisphere. Tundra is largely restricted to the northern hemisphere; there simply is no comparable land mass in the southern hemisphere with the appropriate climate. The areas of the southern hemisphere at high enough latitudes is small, and these areas have their temperatures moderated by the proximity of surrounding oceans. Parts of Greenland extend north far enough that the tundra is replaced by snow and ice; in contrast Canadian and Russian islands at these latitudes are again influenced by the surrounding oceans and may thus exhibit tundra conditions. It should be noted that a similar habitat, alpine tundra, exists in mountains of the alpine biome.

Indicator Plant Species:

A wide variety of plants species can be found on the tundra, as can be seen in the accompanying pictures. What most of them have in common are growth characteristics - they tend to grow low to the ground. Among the common types of tundra plants are willows, sedges and grasses, many in dwarf forms compared to their growth forms in warmer climes. Lichens and mosses (far below) are also important, particularly in the harshest climates.

Arctic Tundra Wildflowers - Alaska

Arctic Tundra Wildflowers - Alaska

Lichen

Indicator Animal Species:

Caribou & Reindeer (Rangifer tarandus) are perhaps THE indicator animal species for the tundra. The species, Rangifer tarandus, is panarctic, but differences are seen between the representatives in the Old World and in North America. The Reindeer is the Old World form, it is smaller than the Caribou and has been domesticated. It is herded by northern peoples across Europe and Russia.

The caribou is the North American form. It is larger and still wild. It migrates from summer to winter grazing areas, following the melting of the snow in the spring. A sizeable herd remains in the Arctic National Wildlife Refuge.

Above: Reindeer antlers as the characteristic velvet (the layer of skin, fur and blood vessels that nourish the developing antlers) is being shed at the end of antler development for the year. Both male and female reindeer and caribou have antlers; the females use theirs for defense while the males also use theirs in mating competitions.

Other important tundra animals include musk oxen, wolves, ptarmigan, snow geese, tundra swans, Dall sheep, brown bears (and polar bears near the coast). A number of small rodents and rodent-like animals are crucial parts of this ecosystem as well.

Reindeer (Rangifer tarandus)

Reindeer (Rangifer tarandus)

Ecological Notes:

The ecology of the tundra is controlled by the cold climate and the northern latitude. The former means that a unique soil structure, permafrost, forms and dominates the biology. Permafrost is a layer of soil that remains frozen year-round. The soil above it may thaw during the summer, but the soil below remains frozen and thus biologically inactive. Further, the permafrost forms a barrier; in temperate climes many animals overwinter by burrowing down into the soil to a point below where the soil freezes. This is not possible in the tundra soils, and thus animals must contend with freezing over the winter. It is no accident that there are no reptiles or amphibians in the tundra.

The long day length that accompanies the short summer is a boon to plants, which are able to photosynthesize 24 hours a day in some places. This leads to rapid plant growth. A surprising number of insects are able to endure the harsh winters (many as frost-resistant eggs); these also undergo rapid development in the summer. Many bird species migrate from southern areas to the tundra each year for the reduced competition and plentiful insect harvest; this rich diet enables them to rear their young in an otherwise bleak environment.

Threats:

There aren't a lot of people running out to build houses on the tundra. Development is not a major problem, nor is there much pressure from human populations (although pollution problems near human settlements can be severe; it is a great technical challenge to effect efficient sewage treatment in a cold environment, for instance). The biggest threats come from airborne pollutants, which have brought measurable levels of pollutants such as DDT and PCB's to even remote areas.

The biggest threat, however, is from oil and gas development and the resulting global warming. The Arctic National Wildlife refuge mentioned earlier has the misfortune of sitting on about a 6 month supply of oil. Despite the great difficulty in extracting this oil, corporate interests and their pet politicians just can't seem to let the idea of drilling here go. Instead of promoting fuel conservation, which could easily make up for the oil not retrieved from this arctic paradise, they continue to push the propaganda on the American people that drilling here will somehow offset high oil prices. An more sever threat comes from global warming, however. As the planet warms (a result of burning all that fossil fuel from elsewhere), the permafrost melts and tundra ecosystems collapse. Further, the permafrost contains a significant amount of dead plant material (grown in earlier and warmer times); as the permafrost warms this material begins to decay, releasing even more CO2 into the atmosphere and accelerating global warming.

Tour:

Arctic Tundra and Alaska Pipeline - Alaska

During the short summer, the tundra appears much like a temperate grassland. Ironically, one of the best ways to access the tundra is via the highway that accompanies the Alaska pipeline from Barrow down to Valdez. The section of pipeline seen here is raised off the ground by special stands. These stands are sunk into the permafrost and designed not to conduct heat lest the warmth from the heated oil (the oil has to be heated to thin it enough to pump economically) thaw the permafrost and cause the pipeline to collapse. Raising the pipeline also allow caribou to pass under it freely.

During the summer the snow melts; much is carried away by the streams winding through the tundra (right), other water collects in small lakes and wetlands (below left).

Tundra Stream - Alaska

Arctic Tundra - Alaska

Tundra Stream and Alaska Pipeline - Alaska

Arctic Tundra - Alaska

Arctic Tundra and Mountains- Alaska

All of these tundra shots (except the reindeer, which were photographed at the Cleveland Zoo) were taken by Sarah Beck, Marietta College class of 2001. In the summer of 2000, Sarah worked with the Woods Hole Oceanographic Institute on research they were doing in Alaska. Sarah was gracious enough to share these photos with us until we are able to mount our own expedition to the tundra.